Without limiting the scope of the present invention, its background will be described with reference to outdoor activities. Recreational activities, such as camping and hunting, afford a person an opportunity to escape the hustle and bustle of everyday life and enjoy nature. Being alerted to the intrusion of a two legged or four-legged visitor is essential, whether to avoid surprise during camping or being alerted to the approach of wild game when hunting. Early warning of the arrival or approach of the two legged or four-legged visitor may provide sufficient time for the outdoors man or woman to take appropriate action. Further improvements are warranted in this field.